This invention relates generally to devices and methods for placing a sensor at a selected site within the body of a patient. More particularly, this invention relates to an improved and relatively simple insertion set for quick and easy transcutaneous placement of a flexible thin film sensor of the type used, for example, to obtain blood glucose readings.
In recent years, a variety of electrochemical sensors have been developed for a range of applications, including medical applications for detecting and/or quantifying specific agents in a patient""s blood and other body fluids. As one example, glucose sensors have been developed for use in obtaining an indication of blood glucose levels in a diabetic patient. Such readings can be especially useful in monitoring and/or adjusting a treatment regimen which typically includes regular administration of insulin to the patient. In this regard, blood glucose readings are particularly useful in conjunction with semi-automated medication infusion pumps of the external type, as generally described in U.S. Pat. Nos. 4,562,751; 4,678,408; and 4,685,903; or automated implantable medication infusion pumps, as generally described in U.S. Pat. No. 4,573,994.
Relatively small and flexible electrochemical sensors have been developed for subcutaneous placement of sensor electrodes in direct contact with patient blood or other extracellular fluid, wherein such sensors can be used to obtain periodic readings over an extended period of time. In one form, flexible transcutaneous sensors are constructed in accordance with thin film mask techniques wherein an elongated sensor includes thin film conductive elements encased between flexible insulative layers of polyimide sheet or similar material. Such thin film sensors typically include exposed electrodes at a distal end for subcutaneous placement in direct contact with patient blood or the like, and exposed conductive contact pads at an externally located proximal end for convenient electrical connection with a suitable monitoring device. Such thin film sensors hold significant promise in patient monitoring applications, but unfortunately have been difficult to place transcutaneously with the sensor electrodes in direct contact with patient blood or other body fluid. Improved thin film sensors and related insertion sets are described in commonly assigned U.S. Pat. Nos. 5,390,671; 5,391,250; 5,482,473; 5,299,571; 5,586,553 and 5,568,806, which are incorporated by reference herein.
Notwithstanding the foregoing improvements in and to thin film electrochemical sensors and related transcutaneous insertion sets, there exists an on-going need for further improvements in such insertion sets particularly with respect to facilitated and cost efficient manufacture, improvements in quick and easy transcutaneous placement of the thin film sensor, and simplified attachment of the sensor to a conductive cable or the like for coupling of sensor signals to the associated monitoring device. The present invention fulfills these needs and provides further related advantages.
In accordance with the invention, an improved insertion set is provided for transcutaneously placing a flexible sensor such as a thin film electrochemical sensor at a selected site within the body of a patient. The insertion set comprises a mounting base adapted for seated mounting onto the patient""s skin, in combination with a cap for assembly therewith to cooperatively capture and retain the sensor. A distal segment of the sensor with sensor electrodes thereon is slidably carried by a slotted hollow insertion needle fitted through the assembled mounting base and cap for piercing the patient""s skin to subcutaneously place the sensor electrodes as the mounting base is pressed onto the patient""s skin. The insertion needle can then be slidably withdrawn to leave the sensor electrodes at the desired subcutaneous site. A proximal end of the sensor including conductive contact pads is carried by a cable fitting on the mounting base for slide-fit coupling with a cable connector, with the mounting base and cable connector including snap fit latch members for releasable interconnection.
In the preferred form, the sensor comprises an elongated thin film element with a head at a proximal end thereof including the contact pads seated in a predetermined position and orientation in the cable fitting formed on the mounting base. A proximal segment of the sensor extends from the cable fitting within a recessed channel defined in an upper surface of the mounting base, with the sensor distal segment protruding angularly forwardly and downwardly from the mounting base. The cap is designed for assembly with the mounting base, as by snap fit interconnection therewith, to capture and retain the proximal sensor segment within the recessed channel. In the preferred form, the sensor distal segment and at least a portion of the proximal segment is protectively carried within a cannula. A proximal portion of the cannula is seated within the channel, and a distal cannular portion extends from the mounting base and is slidably carried by the slotted insertion needle as described in U.S. Pat. No. 5,586,553. The insertion needle is slidably fitted through the assembled mounting base and cap, and is connected at its upper end to an enlarged hub for facilitated manipulation thereof. The hub includes keyed alignment surfaces which cooperate with associated alignment or guide surfaces on the assembled base and cap to prevent or minimize needle rotation relative to the sensor and to guide the needle during slide-fit engagement and disengagement therewith.
The cable fitting formed on the mounting base is sized and shaped for slide-fit coupling with a matingly shaped fitting formed on the cable connector, for electrically coupling the sensor contact pads with individual associated conductors of an electrical cable. In the preferred form, the mounting base includes at least one and preferably a plurality of latch arms for snap fit engagement with latch recesses formed on the cable connector to couple the mounting base and cable connector together with their respective fittings properly engaged.
In use, the snap fit latch members permit quick and easy connection of the insertion set mounting base to the cable connector. The insertion set can then be pressed against the patient""s skin so that the insertion needle pierces the skin and carries the cannula with sensor distal segment therein to the desired subcutaneous position. The mounting base is then affixed to the skin, as by suitable adhesive means, and the insertion needle is withdrawn from the patient leaving the cannula and the sensor therein at the selected insertion site. When it is necessary or appropriate to replace with sensor, the used insertion set can be simply removed from the patient to withdraw the sensor from the patient""s skin, followed by detachment of the insertion set from the cable connector for disposal thereof. A replacement insertion set is then coupled to the cable connector and transcutaneously placed on the patient as described above.
Other features and advantages of the invention will become more apparent from the following detailed description, taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the invention.